1. Field of the Invention
The present invention relates to a resonant magnetic coupling type non-contact power transmission technology for transmitting power wirelessly by using resonant magnetic coupling instead of electromagnetic induction or electromagnetic waves. The present invention also relates to a power generation system for increasing the voltage of electric energy that has been generated by a power generating section such as a solar cell by the resonant magnetic coupling type non-contact power transmission technology.
2. Description of the Related Art
Recently, people have been paying more and more attention to solar power generation. In fact, a power plant for generating a lot of electric power by installing a huge number of solar power generators (i.e., so-called “solar cells”, which will be sometimes simply referred to herein as “cells”) in a wide area has become a reality.
A solar power generation system ordinarily uses a so-called “solar cell module” in which a huge number of cells are arranged inside a metallic module frame and connected together. A glass plate is arranged in front of the solar cell module (which will be simply referred to herein as a “module”) so that the respective cells operate without being exposed to the air. And by assembling a number of such solar cell modules together, a solar power generation system can be established.
Use of such a solar power generation system, however, has not been widespread yet because the cost of manufacturing those modules, power conditioners and other components is too high, which is one of the major obstacles to its introduction. On top of that, the cost of establishing such a system by installing those modules is also too high to neglect. Among other things, the higher the altitude of the place of installation, the riskier and the more expensive the installation work will be, which is a serious problem to overcome in order to further popularize the solar power generation system.
As will be described later, in a conventional solar power generation system, the output voltage of each of its cells is so low that a great many solar cells should be connected together in series to obtain a voltage that is high enough to operate an electronic device or to output a utility grid voltage to sell and buy. If some of those solar cells that are connected together in series went out of order or exposed to a partial shade, the output power of the overall system would decline. And the presence of such a very large number of connection points is a decisive factor in the decline of the long-term reliability of the overall system. In addition, if those modules and cables deteriorate with a long-term use, their replacements should also be installed at such a height. Consequently, the cost of maintenance of the overall system will also rise.
To avoid throwing such a partial shade on the surface of a module, the terminals of the module are arranged on the back surface of the module, and therefore, the module terminals should be wired together on the back surface of the module, too. On the other hand, to generate as much electric power as possible, the modules should be arranged closely to each other with substantially no gaps left between them. Furthermore, as the areas of those modules have been further increasing lately, the work of connecting those big modules with cables at such a height have become even riskier and even more difficult these days.
As a conventional solar power generator that would overcome such problems, a power supply system for supplying energy wirelessly from outside of a building and through the walls of the building has been proposed (see Japanese Patent Application Laid-Open Publication No. 2006-136045 (Embodiment 5 and FIG. 16), for example). Such a power supply system transmits RF (radio frequency) energy through the walls by electromagnetic induction.
On the other hand, in another conventional solar power generator, a technique for connecting together those modules more simply has been proposed (see Japanese Patent Application Laid-Open Publication No. 9-275644 (FIGS. 4 and 5)). In the power supply system, the modules are connected together in series or in parallel by electromagnetic induction.
On the other hand, United States Patent Application Publication No. 2008/0278264 (FIGS. 11B and 14) discloses a new type of wireless energy transfer system for transferring energy wirelessly (through a space) from one of two resonators to the other, and vice versa. That wireless energy transfer system couples those two resonators with each other via the evanescent tail of the oscillation energy of the resonant frequency that is produced in the space surrounding those two resonators, thereby transferring the oscillation energy wirelessly (i.e., by a non-contact method).
The solar power generation system that uses the electromagnetic induction technology as disclosed in Japanese Patent Application Laid-Open Publications No. 2006-136045 and No. 9-275644, however, cannot overcome the solar power generation device's own problem that the output voltage of each cell is low. In the field of solar power generation, a crystalline silicon based solar cell, which is currently used broadly due to its high energy conversion efficiency, has an output voltage Vc of just about 0.5 V, which is very low. For example, if the DC output of a solar power generating section needs to be converted into an AC power of about 200 V, the operation efficiency of a normal power conditioner should be maximized with low distortion characteristic realized in response to an input voltage of at least approximately 350 Vdc. Consequently, to increase the output voltage of the solar power generating section to approximately 350 V, as many as several hundreds of cells should be connected together in series.
It should be noted that even if the DC voltage is not converted into AC power through frequency conversion within such a solar power generation system, a similar problem will also arise. For example, in a DC power supply system that has attracted a lot of attention these days, its working voltage will be either 48 Vdc or within the range of 300 to 400 Vdc. That is why even when solar energy needs to be supplied to a DC power supply system, several tens to several hundreds of solar cells also need to be connected together in series.
However, the greater the number of cells or modules to be connected in series together in a system, the more easily the overall performance of the system will decline due to either so-called “partial shading” (i.e., some of the installation zone goes into the shade) or deterioration in the property of some of those cells or modules to be installed. To overcome such a problem, normally a countermeasure such as introduction of a bypass diode into each module is taken. Such a measure is not preferred because an excessive quantity of heat will be generated or the cost will rise significantly in that case. Meanwhile, even when the voltage needs to be increased using a normal DC/DC converter with a voltage boosting function, it is also difficult to achieve efficiently a voltage step-up ratio that is high enough to significantly reduce the number of cells to be connected in series together.
Also, the voltage boosting characteristic of the wireless energy transfer system disclosed in Japanese Patent Application Laid-Open Publication No. 9-275644 is nothing but a slight improvement achieved by the conventional transformer technology, and is not effective enough to overcome the problems to be solved by the present invention.
Furthermore, according to the electromagnetic induction techniques adopted in Japanese Patent Application Laid-Open Publications No. 2006-136045 and No. 9-275644, RF energy can be transmitted over a very short distance from the power transmitting antenna to the power receiving antenna. In addition, its tolerance with respect to a positional shift parallel to the respective faces of the power transmitting and power receiving antennas that are opposed to each other is also too low to transmit power highly efficiently with a realistic arrangement. What is more, the characteristic of a transformer that can be used in the conventional electromagnetic induction technology is mere an ideal one. That is why to increase the input or output voltage at a high rate, the number of turns should also be set to be a very high value.
Likewise, the voltage boosting characteristic of the wireless energy transfer system disclosed in United States Patent Application Publication No. 2008/0278264 is too nothing but a slight improvement achieved by the conventional transformer technology, and is not effective enough to overcome the problems to be solved by the present invention, either.